An attritor of the type described can have at least one shaft seal hermetically sealing the shaft of the rotor relative to the housing and can include a closeable port which can be used alternatively as a filling or discharge opening.
Such an attritor is described, for example, in U.S. Pat. No. 5,464,163 corresponding to German Patent Document DE 43 07 083 A1 in which the shaft is sealed at the location at which it is journalled in the housing. Another system of this type is described in U.S. Pat. No. 5,678,776.
The improvement described in U.S. Pat. No. 5,464,163 provides that the shaft seal, the bearing and an end wall of the vessel forms a unit on which different vessels can be mounted.
The apparatus described in these patents generally comminutes a charge of the material to be comminuted, discontinuously. In practice, the fully milled product can be emptied from the vessel along with coarser incompletely milled product. Since the system is operated in a batch mode, clump formation cannot be avoided and aggregates of a product, resulting from magnetic forces or Van der waal's adhesion forces can result. As a result of these clumps, the comminution process is not only delayed, but the clumps can interfere with discharge from the vessel and in the case of incomplete emptying of the vessel at the close of milling process, expensive cleaning operations may be required for the milling vessel and the milling bodies.